Microsoft's Surface 2 and Surface Pro 2 tablets may be selling better than their first generation counterparts, but revenues from the Windows RT and 8.1 devices are still not making up for the amount of money the company is spending on its PC hardware products.

According to the latest filing from Microsoft to the U.S Securities and Exchange Commission, revenues from the Surface division came in at $494 million for the three-month time period that ended March 31st. That's up more than 50 percent from the same period a year ago. However, Microsoft spent $539 million to make those tablets and related accessories from January to March, which meant that for the last quarter the Surface group lost $45 million.

Microsoft said that for the nine month period that ended on March 31st, the Surface division generated $1.8 billion in revenue, but $2.1 billion was spent on the business itself. That means the Surface division lost $300 million in the last nine months.

To be fair, it would appear that Microsoft is losing less money each quarter on Surface tablets, but it has yet to make any profit for the company. Perhaps the rumored launch of the smaller Surface Mini could solve that problem.